This invention relates to color television receiver setup circuits.
In order to provide optimum operation of a color kinescope in a television receiver, certain controls associated therewith are adjusted in accordance with a procedure commonly referred to as a kinescope setup procedure. Basically, the setup procedure corrects for certain variations in television receiver operation caused by the multigun, multiphosphor nature of the kinescope. Such variations partly depend upon the cutoff characteristics of the electron guns and the efficiency of the respective phosphors. A function of the setup procedure is to obtain a maximally bright display and at the same time maintain the correct white color temperature at all brightness levels.
Many television receivers include service or setup switches which enable the operator to perform the setup procedure without requiring complicated test equipment. Such switching arrangements provide the capability for selectively switching the receiver from its normal operating mode to a service mode in which illustratively:
1. THE NORMAL VIDEO CHANNEL DRIVE TO THE KINESCOPE CATHODES IS DISABLED;
2. A PREDETERMINED REFERENCE BLACK LEVEL VOLTAGE IS APPLIED TO EACH OF THE KINESCOPE CATHODES; AND
3. THE RECEIVER'S VERTICAL DEFLECTION CIRCUITRY IS DISABLED TO PERMIT CRITICAL ADJUSTMENT OF THE CUTOFF POTENTIAL OF EACH GUN BY OBSERVING THE HORIZONTAL SCAN LINES AT THE CENTER OF THE VIEWING SCREEN.
In many television receiver circuits, the bias voltages to the cathode and control electrodes of each electron gun are derived from the voltages appearing across secondary windings of the horizontal output transformer. If these transformer voltages change when switching from normal mode to service mode of operation, the cutoff and white color temperature characteristics established in the service mode will objectionally differ from the normal mode of operation. It is, therefore, desirable to maintain the aforementioned transformer voltages substantially unchanged in both modes of television receiver operation.